A quick search: "BAK is a file extension for a file format typically used when creating a backup copy of a file. Normally, a BAK file is created as an automatic backup when an application is editing or making changes to the file in question."
On a Mac since 1984. Currently: 24" M1 iMac, M2 Pro Mac mini with 27" BenQ monitor, M2 Macbook Air, MacOS 14.x; iPhones, iPods (yes, still) and iPads.
